Sn1 and E1 reactions

Question 1

overview of Sn1 reaction

Answer 1

• 2-step reaction
• formation of carbocation with LG departure, then nucleophile attacks

Question 2

stereochemistry in Sn1 reactions

Answer 2

• carbocation is planar and stereochemistry is lost
• resulting product is racemic mixture!

Question 3

what is needed for SN1 reactions

Answer 3

• good LG
• more stable carbocation (lowers Ea and is this more reactive)

Question 4

what stabilizes a carbocation?

Answer 4

• more substituted LGs: more electrons from CH3 groups pulled towards cation to stabilize it
• hyperconjugation: nearby C-H sigma bonds (also from more substitution) donate e- to empty pi orbital
• resonance delocalization
• more polar solvents and protic solvents!

Question 5

when is E1 favored over Sn1?

Answer 5

• at high temps
• with tertiary amines (won’t attack as a nucleophile)

Question 6

similarities between Sn1 and E1

Answer 6

• cationic intermediate–reaction begins with loss of LG
• unimolecular RDS
• good LG
• alpha carbon should be secondary or tertiary (makes carbocation more stable and thus lower Ea)
• polar protic solvents
• strength of nucleophile/base isn’t important, and they are often the solvent